Obesity is a major health problem, affecting over one-third of US adults. Behavioral weight control programs are the treatment of choice for mild and moderate obesity, but there is marked variability among patients in the weight losses achieved and the maximum weight losses are usually achieved by month 6, followed by weight regain. Both of these problems might be improved by a more specialized approach for the sub-group of obese patients who report a tendency to overeat in response to emotional and/or cognitive stressors, referred to as internal disinhibition. Recent studies show that approximately 50% of individuals entering behavioral weight loss programs report problems with internal disinhibition and that these individuals lose significantly less weight, particularly at 18 months, than other participants in standard behavioral weight loss programs. We hypothesize that these individuals might achieve better weight loss outcomes in a behavioral weight loss program that focuses on acceptance-based strategies rather than in a standard weight loss program. Acceptance based approaches teach patients to experience thoughts and feelings as they are, without attempting to control them and to continue to pursue their behavioral goals despite experiencing these negative thoughts and feelings, whereas standard behavioral programs teach patients to control their negative thoughts with techniques such as cognitive restructuring and distraction. Acceptance based approaches have yielded positive results for a variety of psychological and health conditions. In a pilot study we conducted, we obtained impressive results using an acceptance based behavioral intervention for obese patients who reported problems dealing with negative internal cues. We propose to conduct a randomized controlled trial comparing a standard behavioral weight loss treatment program (SBT) with an innovative approach that combines standard behavioral weight loss with an acceptance based behavioral intervention (ABBI). We will recruit 160 overweight/obese patients who report high internal disinhibition, and thus would be likely to benefit most from this novel approach to emotion regulation. These participants will be randomly assigned to 18 months of either SBT or ABBI with full assessments at baseline, 6, 12, and 18 months. The primary hypothesis is that participants in the ABBI program will achieve better weight losses than SBT at 6, 12, and 18 months. Secondary hypotheses are that participants in the ABBI program will report greater acceptance of negative thoughts and emotions and greater distress tolerance and will have better treatment adherence than participants in SBT, and that differences in acceptance of negative thoughts and emotions will mediate the differences in weight loss between the groups. This project uses an innovative approach to the treatment of obese individuals who report problems with internal disinhibition. Development of an approach that improves weight loss outcomes would provide a tremendous benefit to the field of obesity.